I got my son's done about 2 weeks before he turned one. He never cooperated with professional photographers, in fact his 1yr old pics (done at Picture People) he cried so hard, I ended up choosing the best one out of 15 shots, and then I had to make it black and white so you couldn't see how red his face was! So now, I take all pictures of him off my digital, no more studios. I would take her several weeks before she turns 2, just in case she has a fit like my son did : )
As far as baby pics...I usually followed the pattern 3 mos, 6 mos, 9 mons, and 1 year and then every year thereafter. I usually did it close to the milestone date....I can't say it was ever exactly on that date, but a week or so before or after.
I like JC Penney's foto studio. You get a long a bang for the buck. I think they're fairly reasonable. Lots of time they have online coupons.